Foundations for buildings and other structures that have settled in the earth after initial construction tend to cause movement of the building structure, deterioration to the building structure, and might require a lifting force to stabilize the building structure. The cause for foundations settling or sinking can be from many sources, such as shifting soils resulting from acts of God or from earth excavation by man, faulty foundation design, water drainage from rain, broken water pipes or other water sources that cause erosion, or just by poor initial construction practices. Resolving and correcting the building settlement problems can be costly to the building owner.
Slab or turn-down slab foundations are installed in certain geographical areas in order to take advantage of the support bearing characteristics of the underlying soils, or as a cheaper, more economical means of supporting a structure over other conventional means of foundation construction practices.
Some turn-down slab foundations that have experienced settlement can be stabilized by installing grout under pressure beneath the slab in order to raise or stabilize the slab when underpinning practices that are currently utilized do not provide proper stabilization for the slab. The grouting of a slab is occasionally a costly form of remediation and usually is not an exacting method of correcting the problem. Grouting with a cementitious material is sometimes unreliable in attempting to correct the settlement problem and, in some cases, can cause additional problems.
For example, grouting is sometimes considered as only a temporary fix, even when the application of grout has properly stabilized the structural slab. There still might be some likelihood of continued erosion and/or shifting of the earth, including the shifting about the grout installed beneath the slab. This tends to allow continued movement of the slab. Also, it usually is not practical to determine if all the voids beneath the slab are properly filled with grout. In some instances, the grout that is placed beneath the structural slab is more dense than the soil and tends to sink within the soil. Moreover, the insertion of grout can damage the structural slab by inadvertently lifting the slab due to the excess pressure of the grout applied by the grout pump. In addition, the application of grout is costly and the grout is likely to follow the paths of least resistance that may not be effective in raising the foundation slab.
In contrast to the stabilizing of a foundation slab with grout, mechanical jack devices can be used for stabilizing the slabs. Ground anchors are inserted in the ground about the portion of the slab to be stabilized so as to function as piles, and foundation-lifting brackets are mounted on the piles and are applied to slab. Jacks are used to raise the foundation lifting brackets with respect to the piles, resulting in applied lifting force to the slab. This keeps the excavation at the slab to a minimum and potentially out of the water table, holds a designed load in a specific soil, and has been proven in field tests to be more rigid, stable and predictable than the use of grout.
Examples of such slab stabilization devices are described in U.S. Pat. Nos. 5,120,163; and 5,213,448.
One of the problems with the prior art mechanical slab stabilization devices is that after the slab has been stabilized the components of the stabilization devices usually protrude above the slab at the edge of the building structure. There is a need to keep the top of the foundation-lifting bracket and its associated components that are mounted to the slab at a level lower than the upper surface of the slab, without sacrificing the strength of the foundation-lifting bracket and its related components. This lower profile arrangement avoids the objectionable upward protrusion of components of the devices that would be obnoxious to the visual appearance of the building structure and would avoid the possible reduced value of the building structure. By reducing the height of the foundation-lifting bracket and its associated components, they can be covered over with earth and become invisible.
As described in the above noted patents, prior art devices used for stabilizing structural foundations of buildings utilize hydraulic jacks that rest upon the power installed pile and lift an assembly of brackets that are connected downwardly to the foundation pile, thereby lifting the bracket and the foundation supported by the bracket. Once the foundation has been lifted to the desired position, the screws of the lifting apparatus are fixed in place and the jack and its associated components are removed from the structure. While this removes the jack and its components from sight, the prior art foundation-lifting bracket has permanent components that still extend too high about the foundation of the building structure.
In some instances, the operators of this type foundation-lifting apparatus have use shims placed on the lifting brackets to achieve the desired lift of the foundation but avoid having the apparatus protrude above grade. However, the addition of shims to the lifting brackets is undesirable since proper sized shims are not readily available and thew shims might shift during the lifting procedures or at a later time.
It is to this problem that this invention is addressed.